1. Technical Field
The present invention relates to an image acquisition device, a biometric authentication device, and an electronic apparatus which are suitable for personal authentication by photographing vein patterns of a human body.
2. Related Art
As a technology of performing personal authentication using human biological information, a technology which uses the vein patterns of fingers has been introduced in the ATMs of banks, and has attracted attention. An authentication method using the vein patterns of fingers has no psychological resistance, since it is not associated with a criminal investigation as are fingerprints, nor does it directly irradiate the eyeball with light like iris recognition. In addition, it has an advantage that it is difficult to counterfeit, since it is internal features not a biological surface which can be readily observed.
Such vein patterns of fingers, which are within an organism, are obtained by illuminating the finger with near infrared light which is highly transmissive to an organism, and by photographing the finger using a camera, an image sensor, or the like, which are sensitive to the near infrared light. Since hemoglobin in the blood absorbs the near infrared light well, the light is absorbed in the blood vessels, and is photographed darkly compared to surrounding tissues. A pattern due to the difference between light and dark becomes the vein patterns.
As an example of this type of finger vein authentication device in the related art, for example, an authentication device described in JP-A-2004-265269 is exemplified. The authentication device described in JP-A-2004-265269 photographs the vein patterns of finger by irradiating the finger with the near infrared light from the right and left of the finger which is placed along a guide.
Meanwhile, along with spread of mobile devices, there has been a growing need for conducting financial settlement using mobile devices. For example, a mobile phone has been one financial payment terminal, and as one personal authentication method which is necessary for the financial payment, finger vein authentication has attracted attention. Currently, slimming of the housing of the mobile phone has progressed, in addition, the mobile phone is also used outdoors, it is necessary for a device photographing finger vein patterns which is mounted to the mobile phone to be slim and to have environmental resistance performance.
Regarding the environmental resistance performance to environment, the presence of light other than the near infrared light for photographing, that is, ambient light such as sunlight has a significant impact on the quality of photographed vein patterns. For example, it is a case where the sunlight is radiated to the finger as the photographing target, or the like. In the sunlight, not only visible wavelength, but near infrared wavelength is included, and the light intensity thereof is much larger than the light intensity of the near infrared light source for photographing the vein patterns. Accordingly, when the sunlight is radiated to the finger, the imaging unit is saturated, and the vein patterns become an overexposed image, being affected by the intense visible light which is included in the sunlight, and the near infrared light. Accordingly, it is difficult to perform the authentication.
For solving these problems, an example in which a band pass filter, or a visible light cut filter is built into an optical system is described in JP-A-2008-168118, JP-A-2009-238205, and JP-A-2009-172263. In JP-A-2008-168118, a method is disclosed, in which a microlens substrate also functions as the visible light cut filter, and in JP-A-2009-238205, a method is disclosed in which the visible light cut filter is built into the microlens array. In addition, in JP-A-2009-172263, a method of forming the lens in the band pass filter is disclosed.
However, since the light intensity of the near infrared light included in the sunlight is larger than the light intensity of the near infrared light for photographing the vein patterns, even if the visible light cut filter is used, the imaging unit is saturated, the vein patterns become the overexposed image, accordingly, the inconvenience of authentication becoming disabled may occur.
In addition, in general, since the band pass filter is formed of dielectric multilayer film (interference filter), multilayer film cut filter, or a color glass, the filter itself becomes thick, and the thickness of the device is increased. Further, since the filter is expensive, it leads to an increase in the cost of the device. When the band pass filter is formed of a single dielectric multilayer film, the thickness is not increased. However, sub-transmission bands occur at both sides of transmission center wavelength, and the visible light is transmitted. Due to this, the imaging unit is saturated, the vein patterns become the overexposed image, and as a result, the inconvenience of authentication becoming disabled occurs.